Heat insulating structure in piston type compressor

ABSTRACT

A heat insulating structure in a piston type compressor includes a heat insulating member. The piston type compressor includes a cylinder block and a cover housing connected to the cylinder block, a piston is accommodated in a cylinder bore defined in the cylinder block to define a compression chamber. A suction pressure region and a discharge pressure region are defined in the cover housing. The piston is reciprocated in the cylinder bore in accordance with rotation of a rotary shaft so that refrigerant gas is drawn from the suction pressure region to the compression chamber and discharged from the compression chamber to the discharge pressure region. The heat insulating member has a predetermined shape and is located in the cylinder block. The heat insulating member has an inner peripheral surface that defines the cylinder bore.

BACKGROUND OF THE INVENTION

The present invention relates to a heat insulating structure in a pistontype compressor, in which a piston is reciprocated in accordance withthe rotation of a rotary shaft to draw refrigerant gas from a suctionpressure region to a compression chamber as well as to discharge therefrigerant gas from the compression chamber to a discharge pressurechamber.

In a piston type compressor (cf. Unexamined Japanese Patent ApplicationPublication No. 2001-515174), refrigerant gas is introduced into acompression chamber. The temperature of the introduced refrigerant gasin the compression chamber affects the performance of the compressor. Asthe temperature is higher, the density of the refrigerant gas in thecompression chamber is lower, so that the performance of the compressordeteriorates. On the other hand, as the temperature is lower, thedensity of the refrigerant gas in the compression chamber is higher, sothat the performance of the compressor improves.

By compressing the refrigerant gas, its temperature rises. Thus, heat istransmitted from the compressed refrigerant gas to a wall that definesthe compression chamber, and the temperature of the wall rises. Aftercompressing and discharging the refrigerant gas, the refrigerant gas isnewly introduced into the compression chamber. The newly introducedrefrigerant gas receives the heat from the wall, and its temperaturerises. Therefore, if the temperature of the wall substantially rises orthe wall has high heat conductivity, the temperature of the refrigerantgas in the compression chamber substantially rises before compression,and the performance of the compression deteriorates.

The present invention is directed to boosting the heat insulatingcharacteristics of the compression chamber in a piston type compressor.

SUMMARY OF THE INVENTION

According to the present invention, a heat insulating structure in apiston type compressor includes a heat insulating member. The pistontype compressor includes a cylinder block and a cover housing connectedto the cylinder block, a piston is accommodated in a cylinder boredefined in the cylinder block to define a compression chamber. A suctionpressure region and a discharge pressure region are defined in the coverhousing. The piston is reciprocated in the cylinder bore in accordancewith rotation of a rotary shaft so that refrigerant gas is drawn fromthe suction pressure region to the compression chamber and dischargedfrom the compression chamber to the discharge pressure region. The heatinsulating member has a predetermined shape and is located in thecylinder block. The heat insulating member has an inner peripheralsurface that defines the cylinder bore.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel areset forth with particularity in the appended claims. The inventiontogether with objects and advantages thereof, may best be understood byreference to the following description of the presently preferredembodiments together with the accompanying drawings in which:

FIG. 1 is a longitudinal cross-sectional view of a compressor accordingto a first preferred embodiment;

FIG. 2 is a cross-sectional view of the compressor taken along the lineI-I in FIG. 1;

FIG. 3 is a cross-sectional view of the compressor taken along the lineII-II in FIG. 1;

FIG. 4 is a partially enlarged cross-sectional view of the compressorwhen a piston is located at its top dead center according to the firstpreferred embodiment;

FIG. 5 is a partially enlarged cross-sectional view of the compressorwhen the piston is located at its bottom dead center according to thefirst preferred embodiment;

FIG. 6 is a partially enlarged cross-sectional view of a compressoraccording to a second preferred embodiment;

FIG. 7 is a partially enlarged cross-sectional view of a compressoraccording to a third preferred embodiment;

FIG. 8 is a partially enlarged cross-sectional view of a compressoraccording to a fourth preferred embodiment;

FIG. 9A is a partially enlarged cross-sectional view of a compressoraccording to a fifth preferred embodiment;

FIG. 9B is a cross-sectional view of the compressor taken along the lineIII-III in FIG. 9A;

FIG. 10A is a partially enlarged cross-sectional view of a compressoraccording to a sixth preferred embodiment;

FIG. 10B is a cross-sectional view of the compressor taken along theline IV-IV in FIG. 10A;

FIG. 11 is a partially enlarged cross-sectional view of a compressoraccording to a seventh preferred embodiment; and

FIG. 12 is a partially enlarged cross-sectional view of a compressoraccording to an eighth preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first preferred embodiment will be described with reference to FIGS. 1through 5, in which the present invention is applied to a piston typevariable displacement compressor.

As shown in FIG. 1, the housing of a piston type variable displacementcompressor 10 includes a cylinder block 11 of aluminum, a front housing12 of aluminum and a rear housing or cover housing 13 of aluminum. Thefront housing 12 is joined to the front end of the cylinder block 11,and the rear housing 13 is joined to the rear end of the cylinder block11 through a valve plate 14 and gasket type valve forming plates 15, 16.The cylinder block 11, the front housing 12 and the rear housing 13 arecombined by a screw 53. As shown in FIGS. 4 and 5, the valve formingplate 15 includes a metallic plate 152 and rubber layers 153, 154 thatare respectively provided on the surfaces of the metallic plate 152. Ina similar manner, the valve forming plate 16 includes a metallic plate162 and rubber layers 163, 164 that are respectively provided on thesurfaces of the metallic plate 162.

The front housing 12 and the cylinder block 11 define a pressure controlchamber 121 and rotatably support a rotary shaft 18 through radialbearings 19, 20, respectively. The rotary shaft 18 extends in thepressure control chamber 121 and protrudes to the outside therefrom. Therotary shaft 18 receives driving power from a vehicle engine 17 as anexternal drive source through a pulley (not shown) and a belt (notshown).

A lug plate 21 is mounted on the rotary shaft 18, and a swash plate 22is supported on the rotary shaft 18 so as to slide in and incline withrespect to the axial direction of the rotary shaft 18. A connectionmember 23 is mounted on the swash plate 22, and a guide pin 24 ismounted on the connection member 23. A guide hole 211 is formed in thelug plate 21. The head portion of the guide pin 24 is slidably insertedinto the guide hole 211. The cooperation of the guide hole 211 and theguide pin 24 allows the swash plate 22 to incline with respect to theaxial direction of the rotary shaft 18 and to rotate together with therotary shaft 18. The inclination of the swash plate 22 is guided by theslide guide relation between the guide hole 211 and the guide pin 24 andthe slide support of the rotary shaft 18.

As the middle part of the swash plate 22 moves toward the lug plate 21,an inclination angle of the swash plate 22 is increased. The swash plate22 comes into contact with the lug plate 21 to restrict the maximuminclination angle. At the position of the swash plate 22 indicated bythe solid line in FIG. 1, the inclination angle of the swash plate 22 isthe maximum. As the middle part of the swash plate 22 moves toward thecylinder block 11, the inclination angle of the swash plate 22 isdecreased. At the position of the swash plate 22 indicated by thetwo-dot chain line in FIG. 1, the inclination angle of the swash plate22 is the minimum.

As shown in FIGS. 1, 2 and 4, a plurality of holes 111 are formedthrough the cylinder block 11 for forming compression chambers. Acylindrical-shaped heat insulating member 30 of synthetic resin ispress-fitted into each of the hole 111. The inner peripheral surface ofthe cylinder block 21 that defines the hole 111 is covered by the heatinsulating member 30.

A piston 25 of aluminum is accommodated in each of the heat insulatingmembers 30. Only one piston 25 is shown in FIG. 2. The piston 25includes a cylindrical-shaped head portion 252 and a neck portion 253 asshown in FIG. 1. The head portion 252 is inserted into the heatinsulating member 30, and the neck portion 253 is engaged with the swashplate 22 through a pair of shoes 26. The rotational movement of theswash plate 22 is converted into the reciprocating movement of thepiston 25, and the piston 25 is reciprocated in the heat insulatingmember 25. The inside of the heat insulating member 30 is a cylinderbore 43 for reciprocating the piston 25 therein, and the heat insulatingmember 30 has an inner peripheral surface 431 that defines the cylinderbore 43 as shown in FIGS. 2 and 3. A compression chamber 112 is definedby the piston 25, the heat insulating member 30 and the valve formingplate 15 in the inside of the heat insulating member 30 (the cylinderbore 43) as shown in FIG. 1. FIG. 5 shows a state where the piston 25 islocated at its bottom dead center.

As shown in FIGS. 1 and 3, the rear housing 13 and the valve plate 14define a suction chamber or suction pressure region 27 and a dischargechamber or discharge pressure region 28 that are separated by an annularpartition wall 29. The suction chamber 27 is located on the radiallyouter side of the rear housing 13 and surrounds the discharge chamber 28around an axial line 181 of the rotary shaft 18. The compression chamber112 is separated from the suction chamber 27 and the discharge chamber28 by the valve plate 14. The valve forming plates 15, 16 and a retainer31 are combined with the valve plate 14 by a screw 32.

As shown in FIGS. 4 and 5, a suction port 141 is formed in the valveplate 14 and the valve forming plate 16, and a discharge port 142 isformed in the valve plate 14 and the valve forming plate 15. A suctionvalve 151 is formed in the valve forming plate 15, and a discharge valve161 is formed in the valve forming plate 16. Gaseous refrigerant in thesuction chamber 27 pushes away the suction valve 151 and is drawn intothe compression chamber 112 through the suction port 141 by the movementof the piston 25 from the right to the left as seen in FIG. 1.

A regulating recess 301 is formed on the end face of the heat insulatingmember 30 near the valve forming plate 15, and a metallic member 302 ismounted on the bottom of the regulating recess 301. The suction valve151 comes into contact with the metallic member 302 at the bottom of theregulating member 301 to regulate its opening degree. The drawn gaseousrefrigerant in the compression chamber 112 pushes away the dischargevalve 161 and is discharged into the discharge chamber 28 through thedischarge port 142 by the movement of the piston 25 from the left to theright as seen in FIG. 1. The discharge valve 161 comes into contact withthe retainer 31 to regulate its opening degree.

As shown in FIG. 1, an inlet 33 for introducing the gaseous refrigerantinto the suction chamber 27 and an outlet 34 for discharging the gaseousrefrigerant from the discharge chamber 28 are formed in the rear housing13. The inlet 33 and the outlet 34 is interconnected by an externalrefrigerant circuit 35 on which a heat exchanger 36 for obtaining heatfrom the refrigerant, a fixed throttle 37, a heat exchanger 38 fortransmitting heat from the surrounding air to the refrigerant and anaccumulator 39 are arranged. The accumulator 39 feeds the only gaseousrefrigerant to the compressor 10. The refrigerant in the dischargechamber 28 flows into the suction chamber 27 via the outlet 34, the heatexchanger 36, the fixed throttle 37, the heat exchanger 38, theaccumulator 39 and the inlet 33.

The discharge chamber 28 and the pressure control chamber 121 areinterconnected by a supply passage 40 formed in the cylinder block 11.The pressure control chamber 121 and the suction chamber 27 areinterconnected by a bleed passage 41 formed in the cylinder block 11 andthe rear housing 13. The refrigerant in the pressure control chamber 121flows out to the suction chamber 27 through the bleed passage 41.

An electromagnetic displacement control valve 42 is arranged on thesupply passage 40. When the displacement control valve 42 isde-energized, the displacement control valve 42 is closed so that therefrigerant does not flow from the discharge chamber 28 to the pressurecontrol chamber 121 through the supply passage 40. Since the refrigerantin the pressure control chamber 121 flows out to the suction chamber 27through the bleed passage 41, the pressure in the pressure controlchamber 121 falls. Therefore, the inclination angle of the swash plate22 is increased, and the displacement is increased. When thedisplacement control valve 42 is energized, the displacement controlvalve 42 is opened so that the refrigerant flows from the dischargechamber 28 to the pressure control chamber 121 through the supplypassage 40. Therefore, the pressure in the pressure control chamber 121rises, the inclination angle of the swash plate 22 is decreased and thedisplacement is decreased. In the first preferred embodiment, carbondioxide is used as the refrigerant.

According to the first preferred embodiment, the following advantageouseffects are obtained.

(1-1) In accordance with the movement of the piston 25 from the right tothe left as seen in FIG. 1, the refrigerant gas in the suction chamber27 is drawn into the compression chamber 112 through the suction port141. In accordance wit the movement of the piston 25 from the left tothe right as seen in FIG. 1, the refrigerant gas in the compressionchamber 112 is compressed and discharged into the discharge chamber 28through the discharge port 142. As the refrigerant gas in thecompression chamber 112 is compressed, the temperature thereof rises.However, synthetic resin or the material for the heat insulating member30 has heat conductivity lower than aluminum or the material for thecylinder block 11. Thus, the heat insulating member 30 having the innerperipheral surface 431 that defines the cylinder bore 43 is hard to beheated by the refrigerant gas in the compression chamber 112, and thetemperature of the heat insulating member 30 substantially does notrise. Therefore, a small amount of heat is transmitted from the heatinsulating member 30 to the refrigerant gas that is newly drawn into thecompression chamber 112 after compressing and discharging the previouslydrawn refrigerant gas. Namely, the temperature of the refrigerant gas inthe compression chamber 112 is substantially prevented from beingincreased by the heat insulating member 30. The heat insulating member30 enhances the heat insulating characteristics of the compressionchamber 112 and contributes to the improvement in the performance of thepiston type variable displacement compressor 10.

(1-2) The heat insulating member 30 having a predetermined shape or thecylindrical shape is made thicker to enhance the heat insulationeffectiveness.

(1-3) The heat insulation member 30 is made of synthetic resin that haslow heat conductivity. The heat insulating member 30 reduces the heattransmission from the cylinder block 11 of aluminum, which has high heatconductivity, to the refrigerant gas in the compression chamber 112.Thus, the heat insulating member 30 contributes to the improvement inthe performance of the compressor.

(1-4) If the piston type variable displacement compressor 10 becomesunusable, the heat insulating member 30 is removed from the hole 111 andis recyclable.

(1-5) Carbon dioxide is used as refrigerant under the pressure higherthan when chlorofluorocarbon is used. Thus, small flow rate is required.When the flow rate is small, it is important to prevent the refrigerantgas in the compression chamber 112 from being heated. The piston typevariable displacement compressor 10 using carbon dioxide as therefrigerant is suitable for the application of the present invention.

In the present invention, the following preferred embodiments arepracticed as shown in FIGS. 6 through 12. In these preferredembodiments, similar elements are referred to by the same referencenumerals as the first is preferred embodiment.

In a second preferred embodiment as shown in FIG. 6, a heat insulatingmember 44 includes a cylindrical portion 441 and a flange 442 that islocated at the end of the cylindrical portion 441 near the valve plate14 and is integrated with the cylindrical portion 441. The cylindricalportion 441 is inserted into the hole 111, and the flange 442 issandwiched between the cylinder block 11 and the valve plate 14. Sincethe flange 442 is sandwiched between the cylinder block 11 and the valveplate 14, the cylindrical portion 441 is held in the hole 111 withoutfollowing the reciprocating movement of the piston 25.

In a third preferred embodiment as shown in FIG. 7, the cylinder block11 is formed with a protrusion 114 on its inner peripheral surface thatdefines the hole 111. A cylindrical-shaped heat insulating member 45 isinserted into the hole 111 and sandwiched between the protrusion 114 andthe valve plate 14. Thus, the heat insulating member 45 is held in thehole 111 without following the reciprocating movement of the piston 25.

In a fourth preferred embodiment as shown in FIG. 8, a valve formingplate 15A is made of metal, and a seal ring 46 is interposed between thecylinder block 11 and the valve forming plate 15A near the outerperiphery of the cylinder block 11 so as to surround the axial line 181of the rotary shaft 18 and all of the is heat insulating members 44. Theflange 442 of the heat insulating member 44 serves to seal thecompression chamber 112, so that the refrigerant gas is prevented fromleaking along the surface of the valve forming plate 15A from thecompression chamber 112 to a hole 115 that is formed in the cylinderblock 11 for inserting the rotary shaft 18 therein. The seal ring 46prevents the refrigerant gas from leaking along the surface of the valveforming plate 15A from the compression chamber 112 to the outside of thecompressor.

In a fifth preferred embodiment as shown in FIGS. 9A and 9B, a heatinsulating member 47 includes a cylindrical portion 471 and an end wall472. The cylindrical portion 471 is inserted into the hole 111, and theend wall 472 is in contact with the valve forming plate 15A of metal andfaces the top end surface of the piston 25. The heat insulating member47 is sandwiched between the protrusion 114 and the valve plate 14.Thus, the heat insulating member 47 is held in the hole 111 withoutfollowing the reciprocating movement of the piston 25. The end wall 472has formed therein a suction hole 473 facing the suction port 141 and adischarge hole 474 facing the discharge port 142. The refrigerant gas inthe suction chamber 27 is drawn into the compression chamber 112 throughthe suction port 112 and the suction hole 473 while the refrigerant gasin the compression chamber 112 is discharged into the discharge chamber28 through the discharge hole 474 and the discharge port 142. The endwall 472 further improves the heat insulating characteristics of thecompression chamber 112.

In a sixth preferred embodiment as shown in FIGS. 10A and 10B, acylinder block 11 A includes an annular base block 48 of aluminum and anannular block 49 of synthetic resin. The base block 48 includes aradially outer portion 481, a radially inner portion 482 and an end wall483, and the annular block 49 is interposed between the radially outerportion 481 and the radially inner portion 482 to surround the axialline 181 of the rotary shaft 18. A plurality of the cylinder bores 43are formed in the annular block 49. Namely, the annular block 49 or aheat insulating member of synthetic resin has the inner peripheralsurface 431 that defines the cylinder bore 43. The end wall 483 hasformed therein a through hole 484 corresponding to each of the cylinderbore 43. The piston 25 is inserted into the cylinder bore 43 through thethrough hole 484. The above structure, in which a plurality of thecylinder bores 43 are formed in the annular block 49 of heat insulatingmaterial or synthetic resin, is more productive than a structure inwhich a plurality of cylinder bores are respectively formed in aplurality of heat insulating members.

In a seventh preferred embodiment as shown in FIG. 11, the peripheralsurface of the head portion 252 of the piston 25 is covered with acoating layer 50 made of the same material as the heat insulating member45. The structure, in which the heat insulating member 45 and thecoating layer 50 are made of material having the same coefficient oflinear expansion, facilitates control of the clearance between the innerperipheral surface 431 of the heat insulating member 45 and the surfaceof the coating layer 50 in thermal expansion.

In an eighth preferred embodiment as shown in FIG. 12, a disc-shapedheat insulating member 51 is bound to a top end surface 251 of thepiston 25 to cover the top end surface 251. The heat insulating member51 further improves the heat insulating characteristics of thecompression chamber 112.

According to the present invention, the following alternativeembodiments are practicable.

(1) In the seventh preferred embodiment, the coating layer 50 is made ofthe same material as the heat insulating member 45. However, the coatinglayer is made of material that has abrasive resistance higher than theheat insulating member or sliding characteristics better than the heatinsulating member, so that the lifetime of the compressor improves.Furthermore, the coating layer is provided in the other preferredembodiments.

(2) Hard rubber or ceramics is used as material for the heat insulatingmember having the inner peripheral surface that defines the cylinderbore.

(3) The cylindrical-shaped heat insulating member includes two parts, ora radially inner part and a radially outer part that are made ofdifferent synthetic resins. Synthetic resin having high abrasiveresistance (e.g. polytetrafluoroethylene) is used as the synthetic resinfor the radially inner part.

(4) The present invention is applicable to a piston type compressor inwhich the discharge chamber is defined on the outer peripheral side ofthe rear housing 13 so as to surround the suction chamber around theaxial line 181 of the rotary shaft 18.

(5) The present invention is applicable to a piton type fixeddisplacement compressor.

(6) The present invention is applicable to a compressor in whichrefrigerant other than carbon dioxide is used.

The present examples and embodiments are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein but may be modified within the scope of theappended claims.

1. A heat insulating structure in a piston type compressor including acylinder block and a cover housing connected to the cylinder block, apiston being accommodated in a cylinder bore defined in the cylinderblock to define a compression chamber, a suction pressure region and adischarge pressure region being defined in the cover housing, the pistonbeing reciprocated in the cylinder bore in accordance with rotation of arotary shaft so that refrigerant gas is drawn from the suction pressureregion to the compression chamber and discharged from the compressionchamber to the discharge pressure region, comprising: a heat insulatingmember having a predetermined shape and located in the cylinder block,the heat insulating member having an inner peripheral surface thatdefines the cylinder bore.
 2. The heat insulating structure according toclaim 1, wherein a hole is formed in the cylinder block for forming thecompression chamber, the heat insulating member having a cylindricalshape and being inserted into the hole.
 3. The heat insulating structureaccording to claim 2, wherein a valve plate is interposed between thecylinder block and the cover housing to separate the compression chamberfrom the suction pressure region and the discharge pressure region, theheat insulating member including a flange at its end near the valveplate, the flange being sandwiched between the cylinder block and thevalve plate.
 4. The heat insulating structure according to claim 2,wherein a valve forming plate of metal is interposed between the valveplate and the cylinder block, a seal ring being interposed between thevalve forming plate and the cylinder block so as to surround an axialline of the rotary shaft and the heat insulating member.
 5. The heatinsulating structure according to claim 2, wherein a valve plate isinterposed between the cylinder block and the cover housing to separatethe compression chamber from the suction pressure region and thedischarge pressure region, a protrusion being formed on an innerperipheral surface of the cylinder block that defines the hole, the heatinsulating member being sandwiched between the protrusion and the valveplate.
 6. The heat insulating structure according to claim 2, whereinthe heat insulating member includes an end wall that faces a top endsurface of the piston.
 7. The heat insulating structure according toclaim 1, wherein the heat insulating member is an annular block includedin the cylinder block, the annular block surrounds an axial line of therotary shaft, the annular block having the cylinder bore.
 8. The heatinsulating structure according to claim 1, wherein the heat insulatingmember is made of synthetic resin.
 9. The heat insulating structureaccording to claim 1, wherein the heat insulating member is made of oneof hard rubber and ceramics.
 10. The heat insulating structure accordingto claim 1, wherein a top end surface of the piston is covered withanother heat insulating member.
 11. The heat insulating structureaccording to claim 1, wherein the piston includes a head portion havinga peripheral surface, the peripheral surface of the head portion iscovered with a coating layer made of the same material as the heatinsulating member.
 12. The heat insulating structure according to claim1, wherein the refrigerant gas is carbon dioxide.